Question

Which of the following buffer systems would be the best choice to create a buffer with pH = 7.3? a)HC2H3O2/KC2H3O2 b)HClO2/KClO2 c)NH3/NH4Cl d)HClO/KClO

Answer 1

A buffer solution is a solution of weak acid and its salt with strong base or vice-versa.

The ideal pH range of a buffer solution lies between pKa-1< pH < pKa+1 for acidic buffer and

pKb-1 <pH < pKb+1 for basic buffer

a) HC2H3O2 has pKa = 4.76, KC2H3O2 is its salt with strong base KOH

so, ideal buffer pH range is 4.76-1 <pH <4.76+1

so, 3.76 < pH < 5.76

b)

HClO2 has pKa = 1.96, KClO2 is its salt with strong base KOH

so, ideal buffer pH range is 1.96-1 <pH <1.96+1

so, 0.96 < pH < 2.96

c)

NH3 has pKb = 4.75 , NH4Cl is its salt with strong acid HCl

so, ideal buffer pH range is 4.75-1 <pH <4.75+1

so, 3.75 < pH < 5.75

d)

HClO has pKa = 7.53, KClO is its salt with strong base KOH

so, ideal buffer pH range is 7.53-1 <pH <7.53+1

so, 6.53 < pH < 8.53 which matches with our desired pH of 7.3 so, this is the best choice to create the desired buffer.